ETFs saw outflows of $679 million in June, according to State Street Global Advisors, one of the primary sponsors for ETFs. June represented the third month of negative flows so far this year, following back-to-back outflows in February and March.

“This is the greatest number of months with outflows for a year since 2008, and we are only halfway through 2018,” wrote Matthew Bartolini, head of SPDR Americas Research at State Street Global Advisors. “One more month of net outflows and 2018 would tie the record of four reached a few times in the late 90s.”

The June outflows deserve some context. For one thing, monthly redemptions of less than $1 billion represent a drop in the overall bucket, as there are about $4.86 trillion in global ETF assets, according to research firm ETFGI. Furthermore, year-to-date flows remain positive, with more than $124 billion flowing into ETFs over 2018 thus far, including June.

Finally, not every fund category saw an investor retreat last month. Fixed-income ETFs had inflows of nearly $7.5 billion last month; however, this was offset by the $5.86 billion pulled from stock funds (led by international funds, a category with $9.9 billion in outflows), and the $2.1 billion withdrawn from commodity-based products.

“The challenging market environment has clearly constricted momentum and weighed on sentiment. In February and March it was U.S. equities, now the other side of the pond is wiping out,” Bartolini wrote.

If volatility in the equity market persists or grows in the second half of 2018, as many analysts say is likely given the potential headwinds of trade uncertainty and less accommodative monetary policy, that could cause a further retreat from ETFs, which could be enough to turn 2018 flows negative overall. A move away from stock-based funds could easily overwhelm any ongoing preference for bond funds, given the category is far larger. There is $2.83 trillion held in U.S.-listed stock ETFs, according to FactSet, compared with just $618.4 billion in bond funds.

ETF flows can be volatile, particularly as the industry has grown amid a decadelong shift to low-fee and passive products, and away from actively managed mutual funds. Not only do ETF flows loosely track movements in the asset classes they cover, but many institutions use them to establish short-term positions or as a way to hedge their portfolios, which can make it difficult to interpret short-term fluctuations in both inflows and outflows.

Whether ETFs see another month of outflows in 2018 remains to be seen, but the industry is at risk of missing another notable milestone.

At this point last year, ETFs had seen about $250 billion in inflows. Meaning, if ETFs were to extend their streak of breaking the previous year’s record — there were inflows of $466 billion over all of 2017 — that would require some $342 billion flowing into the products over the second half of the year.

As Bartolini noted, “this figure is much larger than the full year flows for any year ever, with the exception of last year’s record-breaking total.”